Tensile stress-dependent collagen XII and fibronectin production by fibroblasts requires separate pathways

Physical biology of cell-substrate interactions under cyclic stretch

Mechanosensitive focal adhesion (FA) complexes mediate dynamic interactions between cells and substrates and regulate cellular function. Integrins in FA complexes link substrate ligands to stress fibers (SFs) and aid load transfer and traction generation. We developed a one-dimensional, multi-scale, stochastic finite element model of a fibroblast on a substrate that includes calcium signaling, SF remodeling, and FA dynamics. We linked stochastic dynamics, describing the formation and clustering of integrins to substrate ligands via motor-clutches, to a continuum level SF contractility model at various locations along the cell length. We quantified changes in cellular responses with substrate stiffness, ligand density, and cyclic stretch. Results show that tractions and integrin recruitments varied along the cell length; tractions were maximum at lamellar regions and reduced to zero at the cell center. Optimal substrate stiffness, based on maximum tractions exerted by the cell, shifted toward stiffer substrates at high ligand densities. Mean tractions varied biphasically with substrate stiffness and peaked at the optimal substrate stiffness. Cytosolic calcium increased monotonically with substrate stiffness and accumulated near lamellipodial regions. Cyclic stretch increased the cytosolic calcium, integrin concentrations, and tractions at lamellipodial and intermediate regions on compliant substrates. The optimal substrate stiffness under stretch shifted toward compliant substrates for a given ligand density. Stretch also caused cell deadhesions beyond a critical substrate stiffness. FA's destabilized on stiff substrates under cyclic stretch. An increase in substrate stiffness and cyclic stretch resulted in higher fibroblast contractility. These results show that chemomechanical coupling is essential in mechanosensing responses underlying cell-substrate interactions.

Collagen type XII is undetectable in keratoconus Bowman's layer

PURPOSE

Corneal biomechanical failure is the hallmark of keratoconus (KC); however, the cause of this failure remains elusive. Collagen type XII (COL12A1), which localises to Bowman's layer (BL), is thought to function in stress-bearing areas, such as BL. Given the putative protective role of COL12A1 in biomechanical stability, this study aims to characterise COL12A1 expression in all corneal layers involved in KC.

METHODS

TaqMan quantitative PCR was performed on 31 corneal epithelium samples of progressive KC and myopic control eyes. Tissue microarrays were constructed using full-thickness corneas from 61 KC cases during keratoplasty and 18 non-KC autopsy eyes and stained with an antibody specific to COL12A1. Additionally, COL12A1 was knocked out in vitro in immortalised HEK293 cells.

RESULTS

COL12A1 expression was reduced at transcript levels in KC epithelium compared with controls (ratio: 0.58, p<0.03). Immunohistochemical studies demonstrated that COL12A1 protein expression in BL was undetectable, with reduced expression in KC epithelium, basement membrane and stroma.

CONCLUSIONS

The apparent absence of COL12A1 in KC BL, together with the functional importance that COL12A1 is thought to have in stress bearing areas, suggests that COL12A1 may play a role in the pathogenesis of KC. Further studies are necessary to investigate the mechanisms that lead to COL12A1 dysregulation in KC.

The Transcriptomics of the Human Vein Transformation After Arteriovenous Fistula Anastomosis Uncovers Layer-Specific Remodeling and Hallmarks of Maturation Failure

Introduction

The molecular transformation of the human preaccess vein after arteriovenous fistula (AVF) creation is poorly understood. This limits our ability to design efficacious therapies to improve maturation outcomes.

Methods

Bulk RNA sequencing (RNA-seq) followed by paired bioinformatic analyses and validation assays were performed in 76 longitudinal vascular biopsies (veins and AVFs) from 38 patients with stage 5 chronic kidney disease or end-stage kidney disease undergoing surgeries for 2-stage AVF creation (19 matured, 19 failed).

Results

A total of 3637 transcripts were differentially expressed between veins and AVFs independent of maturation outcomes, with 80% upregulated in fistulas. The postoperative transcriptome demonstrated transcriptional activation of basement membrane and interstitial extracellular matrix (ECM) components, including preexisting and novel collagens, proteoglycans, hemostasis factors, and angiogenesis regulators. A postoperative intramural cytokine storm involved >80 chemokines, interleukins, and growth factors. Postoperative changes in ECM expression were differentially distributed in the AVF wall, with proteoglycans and fibrillar collagens predominantly found in the intima and media, respectively. Interestingly, upregulated matrisome genes were enough to make a crude separation of AVFs that failed from those with successful maturation. We identified 102 differentially expressed genes (DEGs) in association with AVF maturation failure, including upregulation of network collagen VIII in medial smooth muscle cells (SMCs) and downregulation of endothelial-predominant transcripts and ECM regulators.

Conclusion

This work delineates the molecular changes that characterize venous remodeling after AVF creation and those relevant to maturation failure. We provide an essential framework to streamline translational models and our search for antistenotic therapies.

Sexual Dimorphism in the Extracellular and Pericellular Matrix of Articular Cartilage

OBJECTIVE

Women have a higher prevalence and burden of joint injuries and pathologies involving articular cartilage than men. Although knee injuries affecting young women are on the rise, most studies related to sexual dimorphism target postmenopausal women. We hypothesize that sexual dimorphism in cartilage structure and mechanics is present before menopause, which can contribute to sex disparities in cartilage pathologies.

DESIGN

Bovine knee was used as a model to study healthy adult cartilage. We compared elastic moduli under compression, abundances of extracellular and pericellular matrix (PCM) proteins using proteomics, and PCM constituency with tissue immunofluorescence. The gene expression of matrix-related genes under basal, anabolic, and catabolic conditions was assessed by quantitative polymerase chain reaction (qPCR).

RESULTS

The equilibrium modulus was higher in male cartilage compared with female cartilage. Proteoglycans were not associated with this biomechanical dimorphism. Proteomic and pathway analyses of tissue showed dimorphic enriched pathways in extracellular matrix (ECM)-related proteins in which male cartilage was enriched in matrix interconnectors and crosslinkers that strengthen the ECM network. Moreover, male and female tissue differed in enriched PCM components. Females had more abundance of collagen type VI and decorin, suggesting different PCM mechanics. Furthermore, the activation of regenerative and catabolic function in chondrocytes triggered sex-dependent signatures in gene expression, indicating dimorphic genetic regulation that is dependent on stimulation.

CONCLUSIONS

We provide evidence for sexual dimorphism in cartilage before menopause. Some differences are intrinsic to chondrocytes' gene expression defined by their XX versus XY chromosomal constituency.

Collagen XII Deficiency Increases the Risk of Anterior Cruciate Ligament Injury in Mice

Anterior cruciate ligament (ACL) rupture is a common knee injury for athletes. Although surgical reconstruction is recommended for the treatment of ACL ruptures, 100% functional recovery is unlikely. Therefore, the discovery of risk factors for ACL ruptures may prevent injury. Several studies have reported an association between polymorphisms of the collagen XII gene COL12A1 and ACL rupture. Collagen XII is highly expressed in tendons and ligaments and regulates tissue structure and mechanical property. Therefore, we hypothesized that collagen XII deficiency may cause ACL injury. To elucidate the influence of collagen XII deficiency on ACL, we analyzed a mouse model deficient for Col12a1. Four- to 19-week-old male Col12a1^-/- and wild-type control mice were used for gait analysis; histological and immunofluorescent analysis of collagen XII, and real-time RT-PCR evaluation of Col12a1 mRNA expression. The Col12a1^-/- mice showed an abnormal gait with an approximately 2.7-fold increase in step angle, suggesting altered step alignment. Col12a1^-/- mice displayed 20–60% ACL discontinuities, but 0% discontinuity in the posterior cruciate ligament. No discontinuities in knee ligaments were found in wild-type mice. Collagen XII mRNA expression in the ACL tended to decrease with aging. Our study demonstrates for the first time that collagen XII deficiency increases the risk of ACL injury.

Prenatal muscle forces are necessary for vertebral segmentation and disc structure, but not for notochord involution in mice

Embryonic muscle forces are necessary for normal vertebral development and spinal curvature, but their involvement in intervertebral disc (IVD) development remains unclear. The aim of the current study was to determine how muscle contractions affect (1) notochord involution and vertebral segmentation, and (2) IVD development including the mechanical properties and morphology, as well as collagen fibre alignment in the annulus fibrosus. Muscular dysgenesis (mdg) mice were harvested at three prenatal stages: at Theiler Stage (TS)22 when notochord involution starts, at TS24 when involution is complete, and at TS27 when the IVD is formed. Vertebral and IVD development were characterised using histology, immunofluorescence, and indentation testing. The results revealed that notochord involution and vertebral segmentation occurred independently of muscle contractions between TS22 and TS24. However, in the absence of muscle contractions, we found vertebral fusion in the cervical region at TS27, along with (i) a displacement of the nucleus pulposus towards the dorsal side, (ii) a disruption of the structural arrangement of collagen in the annulus fibrosus, and (iii) an increase in viscous behaviour of the annulus fibrosus. These findings emphasise the important role of mechanical forces during IVD development, and demonstrate a critical role of muscle loading during development to enable proper annulus fibrosus formation. They further suggest a need for mechanical loading in the creation of fibre-reinforced tissue engineering replacement IVDs as a therapy for IVD degeneration.

Stiff stroma increases breast cancer risk by inducing the oncogene ZNF217

Women with dense breasts have an increased lifetime risk of malignancy that has been attributed to a higher epithelial density. Quantitative proteomics, collagen analysis, and mechanical measurements in normal tissue revealed that stroma in the high-density breast contains more oriented, fibrillar collagen that is stiffer and correlates with higher epithelial cell density. microRNA (miR) profiling of breast tissue identified miR-203 as a matrix stiffness-repressed transcript that is downregulated by collagen density and reduced in the breast epithelium of women with high mammographic density. Culture studies demonstrated that ZNF217 mediates a matrix stiffness- and collagen density-induced increase in Akt activity and mammary epithelial cell proliferation. Manipulation of the epithelium in a mouse model of mammographic density supported a causal relationship between stromal stiffness, reduced miR-203, higher levels of the murine homolog Zfp217, and increased Akt activity and mammary epithelial proliferation. ZNF217 was also increased in the normal breast epithelium of women with high mammographic density, correlated positively with epithelial proliferation and density, and inversely with miR-203. The findings identify ZNF217 as a potential target toward which preexisting therapies, such as the Akt inhibitor triciribine, could be used as a chemopreventive agent to reduce cancer risk in women with high mammographic density.

Altered haemodynamics causes aberrations in the epicardium

During embryo development, the heart is the first functioning organ. Although quiescent in the adult, the epicardium is essential during development to form a normal four‐chambered heart. Epicardial‐derived cells contribute to the heart as it develops with fibroblasts and vascular smooth muscle cells. Previous studies have shown that a heartbeat is required for epicardium formation, but no study to our knowledge has shown the effects of haemodynamic changes on the epicardium. Since the aetiologies of many congenital heart defects are unknown, we suggest that an alteration in the heart's haemodynamics might provide an explanatory basis for some of them. To change the heart's haemodynamics, outflow tract (OFT) banding using a double overhang knot was performed on HH21 chick embryos, with harvesting at different developmental stages. The epicardium of the heart was phenotypically and functionally characterised using a range of techniques. Upon alteration of haemodynamics, the epicardium exhibited abnormal morphology at HH29, even though migration of epicardial cells along the surface of the heart was found to be normal between HH24 and HH28. The abnormal epicardial phenotype was exacerbated at HH35 with severe changes in the structure of the extracellular matrix (ECM). A number of genes tied to ECM production were also differentially expressed in HH29 OFT‐banded hearts, including DDR2 and collagen XII. At HH35, the differential expression of these genes was even greater with additional downregulation of collagen I and TCF21. In this study, the epicardium was found to be severely impacted by altered haemodynamics upon OFT banding. The increased volume of the epicardium at HH29, upon OFT‐banding, and the expression changes of ECM markers were the first indicative signs of aberrations in epicardial architecture; by HH35, the phenotype had progressed. The decrease in epicardial thickness at HH35 suggests an increase in tension, with a force acting perpendicular to the surface of the epicardium. Although the developing epicardium and the blood flowing through the heart are separated by the endocardium and myocardium, the data presented here demonstrate that altering the blood flow affects the structure and molecular expression of the epicardial layer. Due to the intrinsic role the epicardium in cardiogenesis, defects in epicardial formation could have a role in the formation of a wide range of congenital heart defects.

Effects of equibiaxial mechanical stretch on extracellular matrix-related gene expression in human calvarial osteoblasts

Mechanical stretch commonly promotes craniofacial suture remodeling during interceptive orthodontics. The mechanical responses of osteoblasts in craniofacial sutures play a role in suture remodeling. Moreover, the extracellular matrix (ECM) produced by osteoblasts is crucial for the transduction of mechanical signals that promote cell differentiation. Therefore, we aimed to investigate the effect of mechanical stretch on cell viability and ECM-related gene-expression changes in human osteoblasts. Human calvarial osteoblasts (HCObs) were subjected to 2% deformation. Caspase activity, MTT, and cell viability assays were used to estimate osteoblast apoptosis, proliferation, and viability, respectively. Real-time RT-PCR (RT² -PCR) arrays were used to assess expression of cytoskeletal-, apoptosis-, osteogenesis-, and ECM-related genes. We found that mechanical stretch significantly increased osteoblast viability and cell proliferation, and decreased the activities of caspases 3 and 7. Moreover, the expression of 18 genes related to osteoblast differentiation, apoptosis, and ECM remodeling changed by more than two-fold in a time-dependent manner. Therefore, mechanical stretch promotes HCOb viability and alters expression of genes that are closely related to suture remodeling under mechanical stretch.

Matrix molecules and skin biology

An extracellular matrix (ECM) is a prerequisite for multicellular life. It is adapted to tissues and constantly undergoes changes to preserve microenvironmental homeostasis. The ECM acts as a structural scaffold that establishes tissue architecture and provides tensile strength. It has cell-instructive functions by serving as a reservoir and presenter of soluble agents, being directly signaling, integrating transmission of mechanical and biological cues, or serving as a co-factor potentiating signaling. The skin contains a highly developed, mechanically tough, but yet flexible ECM. The tissue-specific features of this ECM are largely attributed by minor ECM components. A large number of genetic and acquired ECM diseases with skin manifestations, provide an illustrative testament to the importance of correct assembly of the ECM for dermal homeostasis. Here, we will present the composition and features of the skin ECM during homeostasis and regeneration. We will discuss genetic and acquired ECM diseases affecting skin, and provide a short outlook to therapeutic strategies for them.

Mechano-regulation of collagen biosynthesis in periodontal ligament

Periodontal ligament (PDL) plays critical roles in the development and maintenance of periodontium such as tooth eruption and dissipation of masticatory force. The mechanical properties of PDL are mainly derived from fibrillar type I collagen, the most abundant extracellular component. The biosynthesis of type I collagen is a long, complex process including a number of intra- and extracellular post-translational modifications. The final modification step is the formation of covalent intra- and intermolecular cross-links that provide collagen fibrils with stability and connectivity. It is now clear that collagen post-translational modifications are regulated by groups of specific enzymes and associated molecules in a tissue-specific manner; and these modifications appear to change in response to mechanical force. This review focuses on the effect of mechanical loading on collagen biosynthesis and fibrillogenesis in PDL with emphasis on the post-translational modifications of collagens, which is an important molecular aspect to understand in the field of prosthetic dentistry.

Disentangling the multifactorial contributions of fibronectin, collagen and cyclic strain on MMP expression and extracellular matrix remodeling by fibroblasts

Early wound healing is associated with fibroblasts assembling a provisional fibronectin-rich extracellular matrix (ECM), which is subsequently remodeled and interlaced by type I collagen. This exposes fibroblasts to time-variant sets of matrices during different stages of wound healing. Our goal was thus to gain insight into the ECM-driven functional regulation of human foreskin fibroblasts (HFFs) being either anchored to a fibronectin (Fn) or to a collagen-decorated matrix, in the absence or presence of cyclic mechanical strain. While the cells reoriented in response to the onset of uniaxial cyclic strain, cells assembled exogenously added Fn with a preferential Fn-fiber alignment along their new orientation. Exposure of HFFs to exogenous Fn resulted in an increase in matrix metalloproteinase (MMP) expression levels, i.e. MMP-15 (RT-qPCR), and MMP-9 activity (zymography), while subsequent exposure to collagen slightly reduced MMP-15 expression and MMP-9 activity compared to Fn-exposure alone. Cyclic strain upregulated Fn fibrillogenesis and actin stress fiber formation, but had comparatively little effect on MMP activity. We thus propose that the appearance of collagen might start to steer HFFs towards homeostasis, as it decreased both MMP secretion and the tension of Fn matrix fibrils as assessed by Fluorescence Resonance Energy Transfer. These results suggest that HFFs might have a high ECM remodeling or repair capacity in contact with Fn alone (early event), which is reduced in the presence of Col1 (later event), thereby down-tuning HFF activity, a processes which would be required in a tissue repair process to finally reach tissue homeostasis.

Abnormal corneal endothelial maturation in collagen XII and XIV null mice

PURPOSE

Maturation of the endothelium and the adjacent matrix was characterized in wild-type (WT) mice. The influence of FACIT collagen XII and XIV deficiency on the morphology, maturation, and function of the corneal endothelium was examined.

METHODS

Analysis of the endothelium and Descemet's membrane (DM) was performed using transmission electron microscopy at postnatal day (P)4, P14, and P30 in WT, Col12a1(-/-), Col14a1(-/-), and Col12a1(-/-)/Col14a1(-/-) mice. Endothelial junctions were analyzed using ZO-1. The presence of endothelial-stromal communications was evaluated with phalloidin staining as well as electron microscopy. Finally, corneal thickness was assessed.

RESULTS

A thin DM, clefts between endothelial cells and DM, and large "vacuole-like" structures were present in the endothelial cells of WT mice at P4 but not noted at P30. The endothelia of Col12a1(-/-), Col14a1(-/-), and compound Col12a1(-/-)/Col14a1(-/-) in the P30 cornea maintained the vacuole-like structures seen at P4. A mature endothelial junction pattern was delayed in the null corneas. Expression of ZO-1 in WT endothelia at P14 was diffuse and localized to the basolateral and apical cell membrane. At P30, staining was localized to intercellular junctions. ZO-1 reactivity was patchy in Col12a1(-/-), Col14a1(-/-), and compound Col12a1(-/-)/Col14a1(-/-) corneas at P14 and P30. Stromal thickness was increased in P30 null corneas. Endothelial cell processes were demonstrated penetrating the DM and into the underlying stroma, throughout the entire endothelial layer in the P4 cornea.

CONCLUSIONS

Collagen XII and XIV null mice demonstrate delayed endothelial maturation. The structural alterations suggest functional changes in endothelial function resulting in increased corneal thickness. Endothelial-stromal interactions suggest a pathway for signal transduction.

α11β1 integrin-mediated MMP-13-dependent collagen lattice contraction by fibroblasts: evidence for integrin-coordinated collagen proteolysis

We have previously determined that integrin α11β1 is required on mouse periodontal ligament (PDL) fibroblasts to generate the force needed for incisor eruption. As part of the phenotype of α11(-/-) mice, the incisor PDL (iPDL) is thickened, due to disturbed matrix remodeling. To determine the molecular mechanism behind the disturbed matrix dynamics in the PDL we crossed α11(-/-) mice with the Immortomouse and isolated immortalized iPDL cells. Microarray analysis of iPDL cells cultured inside a 3D collagen gel demonstrated downregulated expression of a number of genes in α11-deficient iPDL cells, including matrix metalloproteinase-13 (MMP-13) and cathepsin K. α11(-/-) iPDL cells in vitro displayed disturbed interactions with collagen I during contraction of attached and floating collagen lattices and furthermore displayed reduced MMP-13 protein expression levels. The MMP-13 specific inhibitor WAY 170523 and the Cathepsin K Inhibitor II both blocked part of the α11 integrin-mediated collagen remodeling. In summary, our data demonstrate that in iPDL fibroblasts the mechanical strain generated by α11β1 integrin regulates molecules involved in collagen matrix dynamics. The positive regulation of α11β1-dependent matrix remodeling, involving MMP-13 and cathepsin K, might also occur in other types of fibroblasts and be an important regulatory mechanism for coordinated extracellular and intracellular collagen turnover in tissue homeostasis.

Quantitative proteomics reveals altered expression of extracellular matrix related proteins of human primary dermal fibroblasts in response to sulfated hyaluronan and collagen applied as artificial extracellular matrix

Fibroblasts are the main matrix producing cells of the dermis and are also strongly regulated by their matrix environment which can be used to improve and guide skin wound healing processes. Here, we systematically investigated the molecular effects on primary dermal fibroblasts in response to high-sulfated hyaluronan [HA] (hsHA) by quantitative proteomics. The comparison of non- and high-sulfated HA revealed regulation of 84 of more than 1,200 quantified proteins. Based on gene enrichment we found that sulfation of HA alters extracellular matrix remodeling. The collagen degrading enzymes cathepsin K, matrix metalloproteinases-2 and -14 were found to be down-regulated on hsHA. Additionally protein expression of thrombospondin-1, decorin, collagen types I and XII were reduced, whereas the expression of trophoblast glycoprotein and collagen type VI were slightly increased. This study demonstrates that global proteomics provides a valuable tool for revealing proteins involved in molecular effects of growth substrates for further material optimization.

Type XII collagen regulates osteoblast polarity and communication during bone formation

Type XII collagen–null mice have fragile bones with disorganized collagen fiber arrangement, decreased bone matrix formation, and delayed osteoblast differentiation.

Differentiated osteoblasts are polarized in regions of bone deposition, demonstrate extensive cell interaction and communication, and are responsible for bone formation and quality. Type XII collagen is a fibril-associated collagen with interrupted triple helices and has been implicated in the osteoblast response to mechanical forces. Type XII collagen is expressed by osteoblasts and localizes to areas of bone formation. A transgenic mouse null for type XII collagen exhibits skeletal abnormalities including shorter, more slender long bones with decreased mechanical strength as well as altered vertebrae structure compared with wild-type mice. Col12a^−/− osteoblasts have decreased bone matrix deposition with delayed maturation indicated by decreased bone matrix protein expression. Compared with controls, Col12a^−/− osteoblasts are disorganized and less polarized with disrupted cell–cell interactions, decreased connexin43 expression, and impaired gap junction function. The data demonstrate important regulatory roles for type XII collagen in osteoblast differentiation and bone matrix formation.

Stiffening of human skin fibroblasts with age

Changes in mechanical properties are an essential characteristic of the aging process of human skin. Previous studies attribute these changes predominantly to the altered collagen and elastin organization and density of the extracellular matrix. Here, we show that individual dermal fibroblasts also exhibit a significant increase in stiffness during aging in vivo. With the laser-based optical cell stretcher we examined the viscoelastic biomechanics of dermal fibroblasts isolated from 14 human donors aged 27 to 80. Increasing age was clearly accompanied by a stiffening of the investigated cells. We found that fibroblasts from old donors exhibited an increase in rigidity of ∼60% with respect to cells of the youngest donors. A FACS analysis of the content of the cytoskeletal polymers shows a shift from monomeric G-actin to polymerized, filamentous F-actin, but no significant changes in the vimentin and microtubule content. The rheological analysis of fibroblast-populated collagen gels demonstrates that cell stiffening directly results in altered viscoelastic properties of the collagen matrix. These results identify a new mechanism that may contribute to the age-related impairment of elastic properties in human skin. The altered mechanical behavior might influence cell functions involving the cytoskeleton, such as contractility, motility, and proliferation, which are essential for reorganization of the extracellular matrix.

The fibroblast integrin alpha11beta1 is induced in a mechanosensitive manner involving activin A and regulates myofibroblast differentiation

Fibrotic tissue is characterized by an overabundance of myofibroblasts. Thus, understanding the factors that induce myofibroblast differentiation is paramount to preventing fibrotic healing. Previous studies have shown that mechanical stress derived from the integrin-mediated interaction between extracellular matrix and the cytoskeleton promotes myofibroblast differentiation. Integrin alpha11beta1 is a collagen receptor on fibroblasts. To determine whether alpha11beta1 can act as a mechanosensor to promote the myofibroblast phenotype, mouse embryonic fibroblasts and human corneal fibroblasts were utilized. We found that alpha11 mRNA and protein levels were up-regulated in mouse embryonic fibroblasts grown in attached three-dimensional collagen gels and conversely down-regulated in cells grown in floating gels. alpha11 up-regulation could be prevented by manually detaching the collagen gels or by cytochalasin D treatment. Furthermore, SB-431542, an inhibitor of signaling via ALK4, ALK5, and ALK7, prevented the up-regulation of alpha11 and the concomitant phosphorylation of Smad3 under attached conditions. In attached gels, TGF-beta1 was secreted in its inactive form but surprisingly not further activated, thus not influencing alpha11 regulation. However, inhibition of activin A attenuated the up-regulation of alpha11. To determine the role of alpha11 in myofibroblast differentiation, human corneal fibroblasts were transfected with small interfering RNA to alpha11, which decreased alpha-smooth muscle actin expression and myofibroblast differentiation. Our data suggest that alpha11beta1 is regulated by cell/matrix stress involving activin A and Smad3 and that alpha11beta1 regulates myofibroblast differentiation.

Cell traction forces direct fibronectin matrix assembly

Interactions between cells and the surrounding matrix are critical to the development and engineering of tissues. We have investigated the role of cell-derived traction forces in the assembly of extracellular matrix using what we believe is a novel assay that allows for simultaneous measurement of traction forces and fibronectin fibril growth at discrete cell-matrix attachment sites. NIH3T3 cells were plated onto arrays of deformable cantilever posts for 2-24 h. Data indicate that developing fibril orientation is guided by the direction of the traction force applied to that fibril. In addition, cells initially establish a spatial distribution of traction forces that is largest at the cell edge and decreases toward the cell center. This distribution progressively shifts from a predominantly peripheral pattern to a more uniform pattern as compressive strain at the cell perimeter decreases with time. The impact of these changes on fibrillogenesis was tested by treating cells with blebbistatin or calyculin A to tonically block or augment, respectively, myosin II activity. Both treatments blocked the inward translation of traction forces, the dissipation of compressive strain, and fibronectin fibrillogenesis over time. These data indicate that dynamic spatial and temporal changes in traction force and local strain may contribute to successful matrix assembly.

Laser induced collagen remodeling: a comparative study in vivo on mouse model

BACKGROUND AND OBJECTIVE

Many lasers have claimed the clinical efficacy on skin rejuvenation. In this study, the mechanisms of laser induced collagen remodeling were explored systematically on a Kunming (KM) mouse model in vivo by comparing the different non-ablative laser effects using four different laser treatment modalities.

MATERIALS AND METHODS

The dorsal skin of KM mice was exposed by depilation before the laser treatments. Four laser treatment modalities were used: the 595-nm pulsed dye laser (PDL) (10 ms), 1,320-nm neodymium-yttrium-aluminum garnet (Nd:YAG) laser (0.35 ms), 1,064-nm Nd:YAG laser with Q-switched (5 ns), and long-pulsed (0.3 ms) mode. Each modality exposed one side of the mouse dorsal skin leaving the other side as the contralateral control. Then skin histology, fibroblast number, and the genesis of collagen type I and III were studied by comparing the treatment site and control site at 1 hour, 1 day, 1 week, 3 weeks, 4 weeks, and 8 weeks after laser treatment. Hydroxyproline content of the skin tissue was measured 4 weeks and 8 weeks after laser exposure.

RESULTS

All laser treatments led to marked improvements in dermal layer thickness and collagen fiber density, and the increase in fibroblast number and hydroxyproline content compared with their own controls. Collagen synthesis and remodeling induced by the Q-switched 1,064-nm laser was most effective 4 weeks after treatment, while there was no significant difference among the other three modalities. Among the new collagen genesis after the different laser treatments, collagen type III increased sharply after the Q-switched 1,064-nm laser treatment whereas more collagen type I was elicited by the other laser treatment modalities.

CONCLUSIONS

The efficacy of photo-mechanical effects in promoting more effectively the synthesis of collagen type III, whereas the photo-thermal effect favored more the formation of collagen type I.

Decreased collagen production in chronologically aged skin: roles of age-dependent alteration in fibroblast function and defective mechanical stimulation

Reduced synthesis of collagen types I and III is characteristic of chronologically aged skin. The present report provides evidence that both cellular fibroblast aging and defective mechanical stimulation in the aged tissue contribute to reduced collagen synthesis. The reduction in collagen synthesis due to fibroblast aging was demonstrated by a lower in vitro production of type I procollagen by dermal fibroblasts isolated from skin of young (18 to 29 years) versus old (80+ years) individuals (82 +/- 16 versus 56 +/- 8 ng/ml; P < 0.05). A reduction in mechanical stimulation in chronologically aged skin was inferred from morphological, ultrastructural, and fluorescence microscopic studies. These studies, comparing dermal sections from young and old individuals, demonstrated a greater percentage of the cell surface attached to collagen fibers (78 +/- 6 versus 58 +/- 8%; P < 0.01) and more extensive cell spreading (1.0 +/- 0.3 vs. 0.5 +/- 0.3; P < 0.05) in young skin compared with old skin. These features are consistent with a lower level of mechanical stimulation on the cells in old versus young skin. Based on the findings presented here, we conclude that reduced collagen synthesis in chronologically aged skin reflects at least two different underlying mechanisms: cellular fibroblast aging and a lower level of mechanical stimulation.

Three-dimensional culture regulates Raf-1 expression to modulate fibronectin matrix assembly

Oncogenic transformation has been associated with decreased fibronectin (FN) matrix assembly. For example, both the HT-1080 fibrosarcoma and MAT-LyLu cell lines fail to assemble a FN matrix when grown in monolayer culture (2-dimensional [2D] system). In this study, we show that these cells regain the ability to assemble a FN matrix when they are grown as aggregates (3-dimensional [3D] system). FN matrix assembly in 3D correlates with decreased Raf-1 protein expression compared with cells grown in monolayer culture. This effect is associated with reduced Raf-1 mRNA levels as determined by quantitative RT-PCR and not proteasome-mediated degradation of endogenous Raf-1. Interestingly, transient expression of a Raf-1 promoter-reporter construct demonstrates increased Raf-1 promoter activity in 3D, suggesting that the transition to 3D culture may modulate Raf-1 mRNA stability. Finally, to confirm that decreased Raf-1 expression results in increased FN matrix assembly, we used both pharmacological and small interfering RNA knockdown of Raf-1. This restored the ability of cells in 2D culture to assemble a FN matrix. Moreover, overexpression of Raf-1 prevented FN matrix assembly by cells cultured in 3D, resulting in decreased aggregate compaction. This work provides new insight into how the cell microenvironment may influence Raf-1 expression to modulate cell-FN interactions in 3D.

The collagen superfamily: from the extracellular matrix to the cell membrane

The collagen superfamily is highly complex and shows a remarkable diversity in molecular and supramolecular organization, tissue distribution and function. However, all its members share a common structural feature, the presence of at least one triple-helical domain, which corresponds to a number of (Gly-X-Y)n repeats (X being frequently proline and Y hydroxyproline) in the amino acid sequence. Several sub-families have been determined according to sequence homologies and to similarities in the structural organization and supramolecular assembly. In the present review, we focus on the newly described fibrillar collagens, fibrillar-associated collagens with interrupted triple helix, membrane collagens and multiplexins. Recent advances in the characterization of proteins containing triple-helical domains but not referred to as collagens are also discussed.

Induction of tenascin-C by cyclic tensile strain versus growth factors: distinct contributions by Rho/ROCK and MAPK signaling pathways

Expression of the extracellular matrix (ECM) protein tenascin-C is induced in fibroblasts by growth factors as well as by tensile strain. Mechanical stress can act on gene regulation directly, or indirectly via the paracrine release of soluble factors by the stimulated cells. To distinguish between these possibilities for tenascin-C, we asked whether cyclic tensile strain and soluble factors, respectively, induced its mRNA via related or separate mechanisms. When cyclic strain was applied to chick embryo fibroblasts cultured on silicone membranes, tenascin-C mRNA and protein levels were increased twofold within 6 h compared to the resting control. Medium conditioned by strained cells did not stimulate tenascin-C mRNA in resting cells. Tenascin-C mRNA in resting cells was increased by serum; however, cyclic strain still caused an additional induction. Likewise, the effect of TGF-beta1 or PDGF-BB was additive to that of cyclic strain, whereas IL-4 or H2O2 (a reactive oxygen species, ROS) did not change tenascin-C mRNA levels. Antagonists for distinct mitogen-activated protein kinases (MAPK) inhibited tenascin-C induction by TGF-beta1 and PDGF-BB, but not by cyclic strain. Conversely, a specific inhibitor of Rho-dependent kinase strongly attenuated the response of tenascin-C mRNA to cyclic strain, but had limited effect on induction by growth factors. The data suggest that regulation of tenascin-C in fibroblasts by cyclic strain occurs independently from soluble mediators and MAPK pathways; however, it requires Rho/ROCK signaling.

Reduced Fibroblast Interaction with Intact Collagen as a Mechanism for Depressed Collagen Synthesis in Photodamaged Skin

This report provides evidence from a number of different approaches (i.e., comparison of cell shape in 1-microm sections of photodamaged versus healthy skin at the light microscopic level; comparison of cell shape and apposition to collagen fibrils in ultrathin sections of the same tissues examined by transmission electron microscopy, and fluorescence staining for adhesion site protein expression and actin filament architecture in frozen tissue sections) that dermal cells in healthy skin are attached to collagen fibrils over a large part of the cell border, have a flattened/spread (two-dimensional) appearance and have abundant actin in their cytoplasm. In contrast, cells in photodamaged skin are often in contact with fragmented collagen or amorphous debris rather than intact collagen, have a collapsed/elongated shape, and have a lower amount of actin. Collagen synthesis is reduced in severely photodamaged skin relative to collagen synthesis in corresponding sun-protected skin (N Engl J Med 329:530, 1993). We hypothesize that fibroblasts in severely damaged skin have less interaction with intact collagen and as a result experience a reduction in mechanical tension. Decreased collagen synthesis is (presumed to be) the result.